The present invention generally relates to high intensity discharge (xe2x80x9cHIDxe2x80x9d) lamps, arc tubes, and methods of manufacture. More specifically, the present invention relates to HID lamps, arc tubes, and methods of manufacture wherein the pressure of the fill gas in the arc tube is greater than one atmosphere at substantially room temperature.
HID lamps have been developed as a point source and are particularly suited for fiber optic lighting systems, projection display, and automotive headlamps. Metal halide lamps with xenon as a fill gas have been favored in many applications because of the instant light capability, relatively long life, and relatively high efficiency in producing white light with good color rendition.
In the manufacture of HID lamps for point sources, it is desirable to obtain a final fill gas pressure which is greater than one atmosphere at substantially room temperature. Final fill gas pressures greater than about five atmospheres are common and fill gas pressures may be as high as about six hundred atmospheres.
In the manufacture of xenon metal halide lamps, it is known to obtain a superatmospheric xenon pressure by freezing an amount of xenon into the light emitting chamber of the lamp prior to sealing the chamber. The volume of xenon frozen into the chamber (when at substantially one atmosphere and room temperature) is larger than the volume of the chamber so that the pressure of the xenon sealed within the chamber is greater than one atmosphere when the temperature of the xenon returns to substantially room temperature. The pressure (in atm) of the fill gas sealed within the chamber at substantially room temperature equals the ratio of the volume of gas frozen into the chamber (at substantially one atmosphere and room temperature) relative to the volume of the chamber.
In the known methods of making superatmospheric arc tubes, the prior art teaches that the interior of the arc tube body must be isolated from an uncontrolled atmosphere once the solid fill material and mercury are introduced into the interior of the arc tube body and the second electrode lead assembly is positioned in the remaining open end portion to prevent oxidation of the metallic components of the second electrode lead assembly during the sealing process of the second end portion.
The prior art teaches that the interior of the arc tube may be isolated from an uncontrolled atmosphere by either (i) placing the arc tube body in a controlled atmosphere such as a glove box as taught in U.S. Pat. No. 5,108,333 to Heider et al. dated Apr. 28, 1992 or (ii) connecting the open end to a vacuum system which provides the necessary seal as taught in U.S. Pat. No. 5,505,648 to Nagasawa et al. dated Apr. 9, 1996.
As disclosed in Heider et al., one end portion of the arc tube body must be long enough to enclose the entire electrode lead assembly when the assembly is positioned within the end portion. Once the arc tube is placed within the controlled atmosphere of the glove box, the body is filled with xenon and then the end portion is fused closed so that the entire electrode lead assembly is enclosed within the body. The arc tube may then be removed from the glove box so that the xenon may be frozen into the chamber and then sealed by shrinking or pinching the second end portion. The excess portion of the end portion is then removed to expose the outer lead of the electrode lead assembly.
The prior art methods suffer from the significant disadvantage of the requirement for isolating the arc tube body from the uncontrolled atmosphere. This has generally required the use of a glove box or vacuum system. Such methods are complex and difficult to automate.
Accordingly, it is an object of the present invention to obviate many of the deficiencies of the prior art and provide a novel HID lamp, arc tube and method of making arc tubes.
It is another object of the present invention to provide a novel arc tube and method of making arc tubes for HID lamps which obviates the need to perform any process steps within a controlled atmosphere.
It is a further object of the present invention to provide a novel arc tube and method of making tipless arc tubes for HID lamps in which the arc tube remains open to an uncontrolled atmosphere during the step of finally sealing the arc tube.
It is yet another object of the present invention to provide a novel arc tube and method of making tipless arc tubes for HID lamps in which communication of an inert fill gas with an uncontrolled atmosphere such as air is maintained until the arc tube is hermetically sealed.
It is yet a further object of the present invention to provide a novel arc tube and method of making arc tubes for HID lamps which obviates the need to remove a portion of the end portion to expose the outer portion of the electrode lead assembly.
It is still another object of the present invention to provide a novel arc tube and method of making arc tubes for HID lamps in which each end portion of the arc tube body has substantially the same length as the end portions of the finished arc tube.
It is still a further object of the present invention to provide a novel apparatus for extending the tubular opening formed by the end portion of an arc tube body and method of making arc tubes for HID lamps.
It is still another object of the present invention to provide a novel arc tube and method of making arc tubes for HID lamps in which the temperature of the fill gas is controlled prior to sealing the arc tube in an uncontrolled atmosphere.
It is yet another object of the present invention to provide a novel arc tube and method of making arc tubes for HID lamps having superatmospheric fill pressure in which there is no pressure differential at the time of sealing.
These and many other objects and advantages of the present invention will be readily apparent to one skilled in the art to which the invention pertains from a perusal of the claims, the appended drawings, and the following detailed description of the preferred embodiments.